If you have under 99,000 miles switch to synthetic. There are 2 ways to do it. One use a blend and the next change go to fully synthetic. If the car has under 49,000 miles just use a 5 minute motor flush and switch to synthetic. Depending how many miles you do in 3 months. If you do about 5000 to 7500 miles switch to Mobil One 5w20 if you do more you can use Mobil One Extended Performance Oil good for 15,000 miles but still change it every 90 days reguardless. The filter should also be changed with every oil change. Do not use regular oil you are killing your engine made to last 300,000 or more miles. I have a 6cyl 2003 EX Coupe with 46,000 miles and a 6cyl 1998 EX Coupe with 231,500 miles and that is all I put in the engine. Both oils are available at Walmart 7500 oil 5 quarts about $23.97 and 15000 oil 5 quarts about $28.97 it is important that once you switch always use the same exact oil. Castrol has a synthetic oil but I believe in Mobil One as I put on almost 200,000 miles on my 98 with this oil and the engine is quiet as silk and performance is strong as new.